This invention relates to fishing tackle. More particularly, it relates to an adjustable swivel base for mounting a downrigger to a fishing boat in a manner which allows the downrigger's boom to be rotated to different angular positions relative to the boats longitudinal axis.
Downriggers are well known systems for trolling at a precise water depth. In the typical set-up, a short boom with a windlass or electric winch is used to lower a heavy lead trolling weight attached to a cable. Since the weight is relatively heavy, it maintains a constant depth throughout speed changes and turns. By contrast, the relatively light artificial lures and baits used for trolling would tend to change depth easily if not used in conjunction with a downrigger system. The fishing line is attached to a release mechanism on the trolling weight, or on the cable, and trails the lure or bait well behind the weight at a controlled depth. Due to variations in the water temperature profile, salinity, oxygen level or bottom structure, fish tend to concentrate at narrow bands of water depth. Controlled depth trolling is a very effective and productive means to catch these fish.
Frequently, the downrigger apparatus has a fishing rod holder mounted near the base of the boom. Several downrigger/rod combinations can be mounted on the sides or stern of a boat, allowing a fisherman to troll with several rigs at once. When a fish strikes one of the rigs, the fisherman can remove that rod from its holder and begin playing the fish. Meanwhile, a mate or another fisherman reels in the other lines and cables to avoid entanglement.
In using multiple downriggers, it is advantageous to point the downrigger booms at different angles along the longitudinal axis of the boat to keep the trolling lines separated. While fixed position mounts can be installed at angles to provide a set configuration, it has been found more convenient to use adjustable swivel mounts. These mounts allow immediate configuration changes, and the convenience of swinging the boom inboard for adjustment of the release clip or removal of the trolling weight. A prior example of such a swiveling downrigger is shown in U.S. Pat. No. 3,937,415 to Prinz.
With many downriggers, the frame, boom, windlass, and rod holder detach from a mounting base which is bolted or screwed onto the boat structure, so that they can be removed and stored when not in use. Consequently, it is advantageous to make the mounting base, rather than the downrigger frame, adjustable to the desired angle. An example of such swivel base mount is shown in U.S. Pat. No. 4,044,489 to Henze. A more recent swivel base mount of that type is the Adjustable Swivel-Matic Base manufactured and sold by Penn Fishing Tackle Mfg. Co. of Philadelphia, PA.